Acoustic feedback oscillations occur at the frequencies of the maximum peak amplitude room response, if the gain and phase conditions are satisfied. Acoustic feedback occurs in wide variety of situations involving microphone, power-amp, and speakers. FIG. 1 shows a typical audio system 100 where acoustic feedback may occur. A microphone 102 receives audio signals such as voice. Components 104-108 process and amplify the received signal for presentation by a speaker 110. The feedback problem begins when the microphone 102 receives the speaker signal that includes an amplified version of the original audio signal received at the microphone 102. That feedback signal is amplified again by the system 100. This process continues until the amplifiers 104 and/or 108 are driven into a saturation state and the sound provided by the speaker becomes unintelligible.
In a real-time sound system, a loud feedback tone appears quickly, without any warning. The acoustic feedback phenomenon is dependent on several conditions: physical position of microphones/headphones/speakers; current overall gain level; acoustical response of the environment; resonant frequency of each transducer in the system.
In general, the problem of headroom improvement versus audio quality is common for all feedback cancellation equipment. Usually, peak amplitude response analysis of all sound elements is sufficient to partially characterize the self-oscillation properties of the feedback-prone audio system.